(a) When a small quantity of liquid is poured in glass, three interfaces namely liquid-air, solid-air and solid-liquid are formed. The surface tensions corresponding to these three interfaces i.e., S_LA, S_SA and S_SL are related to angle of contact θ as,

cosθ = {S_SA - S_SA}/{S_LA}

In case of mercury glass, S_SA < S_SL, therefore, cosθ is in negative or θ > 0, obtuse. In case of water glass. S_SA > S_SL, therefore a cosθ is positive or θ < 90, i.e., acute.

(b) For mercury glass, angle of contact is obtuse. In order to achieve this obtuse value of angle of contact, the mercury tends to form a drop. In  case of water glass, the angle of contact is acute. To achieve this acute value of angle of contact, the wate tends to spread.

(c) Surface tension of liquid is the force acting per unit length on a line drawn tangentially to the liquid. Since this force is independent of the area of liquid surface; therefore, surface tension is also independent of the area of the liquid surface.

(d) We know that the clothes have narrow spaces in the form of capillaries. The rise of liquid in a capillary tube is directly proportional to cosθ. If θ is small, cosθ will be large. Due to which capillary rise will be more and so the detergent will penetrate more in clothes.

(e) In the absence of external forces, the surface of the liquid drop tends to acquire the minimum surface area due to surface tension. Since for a given volume, the surface area of sphere is least, hence a liquid drop takes the spherical shape.